In development researches of pharmaceuticals, nutritional foods, and specified functional foods, and in a variety of basic researches, acquisition of data from experimental animals is essential work. Especially, mouse or rat infants correspond to human immature babies whose eyes and ears have not been opened, and have high sensitivity to drugs and the like because of their immature organs. Therefore, data of high accuracy is expected to be obtained from these animals.
When these experimental animals with a need for suckling such as infants are fed with e.g., milk, a compulsory feeding method is dominantly employed in which a feed is given to a gastrointestinal tract using a gastric probe or a catheter. This method must be employed because in giving milk or a test solution, it is necessary to control the dose amount or the dose interval depending on the purpose of the study. However, according to the above method, invasion to organisms, for example, abraded wounds on the pharynx or esophagus in the case of a gastric probe, and wounds created in attaching a catheter is inevitable. As a result, inflammations caused by damages to viscous walls result in data variation among individuals of experimental animals at higher possibility. In the situation that an experimental animal must take milk or a test solution voluntarily due to the purpose of the study, for example, for developing milk having a specific application, the method using a gastric probe or a catheter which is a compulsory administration method cannot be employed. Apart from the study purpose, use of a gastric probe or a catheter with respect to a mouse or rat infant having a body weight of less than 3 grams will inflict damages on a very soft pharynx, esophagus, or gastric wall by a probe needle or the like at very high possibility.
While accurate data is expected to be obtained by using mouse or rat infants for development of pharmaceuticals or specified purpose milk such as milk for immature baby, practically, there is no method for quantitatively feeding mouse or rat infants with milk or a test solution voluntarily and orally at a single dose or repeatedly in safety.
In the course of developing an administration method of liquid feed or the like to experimental animals, the inventors of the present application have developed an automated artificial feeding device for experimental animals that enables experimental animals to voluntarily drink milk via an artificial nipple or the like without using a gastric probe or the like. This is reported in CONTEMPORARY TOPICS in Laboratory Animal Science Vol. 35-5, p83-86 (1996).
The feature of the automated artificial feeding device lies in a structure of the artificial nipple. The artificial nipple has a double structure so as to prevent milk from leaking when an infant is not drinking the milk. An outer part of the nipple is formed with a cross cutting at its tip end, and an inner part of the nipple is formed with slits at four positions on its lateral side. Also an injection needle having a gauge of 24 to 26G excluding a needle point is inserted into the nipple. The inventors attempted to prevent milk from leaking and to control the flow by combination of these structural features.
Likewise the present invention, this automated artificial feeding device is also designed for an experimental animal to voluntarily stick to the artificial nipple and orally take a liquid feed or the like. However, this device still has the following problems.
1) The previous device is principally designed for rat infants, so that when it is used for mouse infants, it cannot follow the growth of the infant.
2) The above device fails to feed a test solution or the like in such a simple manner as giving milk to an infant while holding the device with hand as is necessary. Although the above device enabled voluntary feeding according to the own will of the rat infant, it is still difficult to give a test solution or the like regularly and quantitatively in a specifically controlled manner in practice of the experiment, for example, to give a test solution according to need.
3) Since the structure of the nipple of this device is too complicated as an artificial nipple for small animals such as mouse and rat, performance variation between nipples is easy to occur, and it is difficult to stabilize a feeding amount or the like.
The complicated structure of the previous artificial nipple was devised for preventing a liquid feed or the like from leaking from the nipple as described above. However, in order to stabilize the feeding amount and to further improve the reliability of the data, it is desired to develop a nipple which is simple in structure in order to replicate the nipples with ease and excellent in performance, a liquid feeding method for experimental animals that is designed to be suited to the nipple, and a device for implementing the same.